The militants have damaged what little infrastructure existed in the country's underdeveloped north at a time when the government is facing a cash crunch as a result of the free-falling oil price.

A week ago, Boko Haram killed 30 people and injured 20 others in raids on three villages near the home of the Nigerian army chief.

An estimated 2,000 women and children have been seized by Boko Haram since January 2014

The jihadists have allied themselves with the Islamic State group, but experts doubt the scale and scope of the collaboration.

Still, there are growing fears that a once localised hardline Muslim movement is morphing into a regional jihadist threat as Boko Haram launches attacks on Nigeria's neighbours Chad, Cameroon and Niger.